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Steepest climb a wingsuit pilot can achieve?
There was a question yesterday about landing in a wingsuit; the main issue is, of course, the high speed, both vertically and horizontally. One way to reduce speed is flaring; another would be to gain height, which apparently is possible: One of the answers there links a video of a wingsuit pilot ascending from a lake bed to the height of the crown of a dam. However, the climb is modest and the pilot actually accelerates beforehand to fly that maneuver, so that the resulting speed after the climb is probably not lower than usual. In order to shed more speed, the climbing angle would have to be steeper. One extreme case of such a landing is "trampwalling" (see e.g. here): A trampoline jumper is able to land safely on a hard surface at the crest of a parabola where their speed is near zero.
My question is in the title: What is the maximum climbing angle that can be achieved with a (potentially modified) wingsuit? If it is steep enough, a lot of kinetic energy could be shed by climbing, and the landing would be much less dangerous, provided the terrain permits. I have created a little sketch of the idea:

You can achieve any angle: it is just "turning up". You lose lift, but with enough speed it is not a problem (for short of time). Like acrobatic aircraft. "Turning" is not a problem. Keeping speed (and so control) and lift is a different question

@GiacomoCatenazzi Well, if you are near-vertical in what resembles a steep parabola flight, lift is not an issue.

This landing would be more dangerous than a flare over a long, flat surface. The slightest misjudgment of the flare could be catastrophic. Flare too late or too little and you slam into the wall at speed, too soon or too much and you stall and slam onto the ground. I appreciate that it's not the core of your question, but if you are thinking about this as a viable way of a wingsuit to land it isn't.

@GdD Yes, I understand that as with all other flying, not much untoward can happen before you get close to the ground, which is why that's typically avoided except when we have to, for landing, and we want to do that as safely as possible. That said, any landing in a wingsuit seems batshit crazy, so the difference seems gradual ;-). I assume one could keep enough distance for necessary corrections from the ascending ground (which implies terrain that rises slower than one's own proven ascent capability) until it's actual landing time.

I don't understand this question. A wingsuit is just a flying device, like any other. With enough speed and enough lifting surfaces it can do a loop. @Peter-ReinstateMonica, with this in mind could you make clearer the limitations we must impose? Otherwise I feel the answer is "Vote to close".

@KennSebesta I was not sure, I have never seen somebody do a looping (and I'm sure they would celebrate it), I cannot find one with my google-fu. "A wingsuit is just a flying device, like any other" may be true but misses the point: With such a terrible glide ratio it seems to be a big deal to achieve any ascent at all. (Could the Space Shuttle perform a looping?)  At least that's what the linked video appears to say. So please, enlighten me, write an answer. You appear to say "the maximum climb angle is 90 degrees". Do I understand you correctly? Can you show a demonstration?

I think this is a valid question. With enough speed anything can do a loop but it is not trivially the case that a wing suit can pick enough speed at terminal velocity to complete such a maneuver.

You know, why not try all this with a larger wing, such as a hang glider.  Birds commonly stall/land on perches, approaching them from below.  A wing suit will give poor (brick-like) gliding characteristics, with not much room for finesse.

@RobertDiGiovanni A bird approaching a perch also quickly modulates drag and (reverse) thrust, and on top of that relies on "brakes" grippier than any pair of sneakers!

@Peter-ReinstateMonica so this basically boils down to "assuming a draggy, airfoil which stalls at a low angle of attack, is there a limit to how high it can point?" This is indeed an interesting question, although I would say that the broader question-- "What is the minimum L/D below which a gliding aircraft attempting a loop will stall before it passes through inverted flight?"-- can likely be answered analytically.

Wrong:  A climb of 64 degrees was momentarily reached by Luke Rogers on Sept. 9, 2018 near Brisbane, Australia.
This was 65 seconds into his flight track,
where the climb rate was 153 km/h and the ground speed was 74 km/h.  The flight track shows that this climb was preceded by an even steeper dive.

Correction:
In many other flight tracks on that website, the second plot's vertical speed is almost always positive.
But common sense, corroborated by the third plot's "Height", says that the wingsuit is usually falling, not rising.
So "vertical speed" is inverted, a surprise for other kinds of aviators.
The steepest climb in this track, then, is where the second plot's red line is well below zero,
and the green line is also low.
At 26 seconds, vertical speed is -91 km/h, and ground speed is 129 km/h.  35 degrees.
(At 56 seconds, -66 and 107, so 32 degrees.)
This flight was intended to maximize the total height of a climb, so for efficiency it probably didn't also maximize climb angle.
Other flight tracks on that website may have steeper climbs.
To find them, one could collect each https://skyderby.io/tracks/99999 (tricky: some numbers are missing), save that .html file, parse spd_chart.series[0] (ground speed) and spd_chart.series[1] (vertical speed),
and at each time point calculate the inverse tangent to get the climb angle.

That's interesting, but I don't understand the reluctance to push the wingsuit to higher angles of attack. If the airspeed were still ~norm<74,153> = 170kph, then there must have been considerable directional control still.

You're right.  Deceleration due to gravity at a climb angle of 64 degrees is already 90% that of a purely vertical climb.  So going a bit steeper for a few seconds (5 seconds is all it takes to go from 170 km/h to 0) hardly matters.

First time I have seen a flight track, but looking at it: Judging by the red line in the second chart, there seem to be two times the vertical speed dipped into the negative, around T=25 seconds and 55s (even though the pop-up numbers stay positive, probably a defect of the software which cannot cope with this unexpected data); a third time it was almost zero, around 89s. That is corroborated by the blue line in the third chart which has a negative slope during that time. Am I misunderstanding something? (At 65s it's your numbers, but vertical seems positive.)

@Peter-ReinstateMonica, good catch.  I've corrected this answer.


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Is there a way I can find out online what private jets are parked tonight at a nearby international airport?
There is an international airport about 10 miles from my home.
Is there any way I can find out online what private jets are parked there tonight? I am not familiar with any of the lingo used here :) so if you could respond in layman's terms I'd greatly appreciate it.

Would seem like a serious invasion of privacy to me.

Companies are certainly tracking corporate jets and selling the data to various entities hoping to trade on the information.

What region are you in? There might be a spotters community active at the airport, logging their sightings online. In the Netherlands, for example, some users of the Scramble Messageboard regularly post which private jets (or "general aviation aircraft") are parked on the apron.

There is not simple list available online, apart from calling the airport and asking them directly. Aircraft are expensive assets so when people own them they tend to keep them under the radar and out of sight and out of the elements by parking them inside a hangar. As an outsider you can only see the outside parked aircraft from the airport fencing.
Determining which aircraft are parked for a short term on an airport is relatively simple to find with the use of an aircraft tracking site such as FlightAware and FR24. On these sites you can enter an airport and see all the official flights in and out of that airport. Flights that have landed but not yet departed will be parked somewhere on the airport.
For example, Lubbock Executive Airpark (Lubbock, Texas, USA)
https://flightaware.com/live/airport/F82/arrivals
Starting from January 2020, the FAA dictates that all airborne flights in the USA should be equipped with an ADS-B transponder, when inside ADS-B airspace, used by the sites above and air traffic control to track flights. So from that day the tracking of smaller aircraft will be greatly improved.

Not all aircraft will be required to use ADS-B. For example, those without electrical systems are exempt, for obvious reasons.

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What is the difference between a standard airworthiness and a experimental airworthiness certificate?
What is an experimental certificate?  Is it just a certificate that is for aircraft that were built experimentally such as home-built aircraft? What is the purpose of the certificate?

All certificated aircraft must be safe to fly. The difference between a type certified aircraft and a experimental certificated aircraft is in how this safety is demonstrated.
A type certificate and associated production certificate requires that all the engineering work and construction processes are compliant with safety regulations. This takes years of work and costs millions of dollars. Since the design and production processes have been shown to be compliant, it is assumed that the aircraft produced using these processes are also safe. Minimal flight testing (less than an hour) is needed before delivery to a customer.
An experimental certificate does just the opposite. No (FAA) scrutiny is applied to either the design or production of the aircraft. Instead, the completed aircraft has to undergo extensive flight testing before being deemed airworthy. Forty hours of flight in a defined, restricted area is required before being allowed leave. This allows people interested in aviation to build and fly aircraft without million dollar budgets.
A production aircraft can be sold to customers and used in money making businesses. An experimental aircraft is for personal use (this could also be limited use by a company) and may not be used for revenue generation. So if you want to (try to) make money with aircraft manufacturing you go production; if you do it for fun you go experimental amateur built.

@757toga Flight time applies to all "unproven" aircraft, amature built or not. See https://www.ecfr.gov/current/title-14/chapter-I/subchapter-F/part-91/subpart-D/section-91.319. The key is that  if you don't certify the design and production, you have to test the result. No third option exists.

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How should you handle a Hazardous Attitude?
As a First Officer, when you sit inside the cockpit to meet the crew but having a talk with the PIC, Do you have a talk explaining that if he makes a wrong decision, you as FO will take controls if it jeopardizes safety?
Reason I asked is because, we are all humans and we are subjected to life outside of flying, what if the captain isn't having a good day etc.. and his judgement is clouded, you offer solutions to the problem but he ignores them and pushes on.
Can you as FO take control?
I guess thats where PIC comes into action but if there be a reason where the PIC isn't making good decisions how can you as a FO handle that situation?

Related, not quite a duplicate: https://aviation.stackexchange.com/q/40777/7532

Do you have a talk explaining that if he makes a wrong decision, you as FO will take controls if it jeopardizes safety?

Sitting in both right and left seat for 20+ years of airline operations, I've never heard anybody say any such thing in a crew briefing, and if somebody did in roughly those terms, I'd have to evaluate whether this pilot has their own set of hazardous attitudes to such an extent that we may not go flying together today.
First, crew briefings are not meant to cover every SOP in the book... they'd be hours long, and even then you'd probably leave something out.  It's important to give the other pilot that you're flying with some idea of where you're at -- new, experienced, by-the-book, hyper-by-the-book, relaxed, stressed, whatever.  But beyond a fairly high level statement of "I'll try to do things with no surprises; if something looks wrong then I'm probably in left field, so laugh at me, ask the question, whatever you need to & I'll get back on track and we'll keep going," I'm not going to hammer the standards too hard.  (It was always a little insulting when a Captain who'd never flown with me started off with "I fly by the book & expect you to do so as well" -- you assume, never having met me, that I wouldn't unless you introduce yourself like that?  Really??)
A default set of assumptions is that when the FO knows what the Captain expects, he can adapt (i.e. is this a 3-day check ride, be on your best behavior, is this "do whatever (within unstated limits)", is this a relaxed but professional middle ground), and I don't need to tell him to "be professional."  And at the same time, he can assume that I didn't wake up today planning to do anything stupid or unsafe.
Obviously, if one pilot slumps over incapacitated, of course the other pilot will take the controls & do whatever's necessary to get the airplane on the ground safely.  Nobody briefs that.
If the FO has a question or a problem with a decision the Captain is making, it's expected that he'll voice his concerns, professionally, and the crew will find a satisfactory solution.  Again, other than a general statement to put an FO at ease that I'm open to those sorts of inputs, that's not typically briefed in great detail by either pilot.
If the two pilots simply can't agree on a course of action, then the situation gets harder.  Legally, the Captain is the Pilot In Command, and the final call is his.  The FO isn't without options, but "I'll take the aircraft from you if I don't like what you're doing" is pretty drastic. As in, if the FO turns out to be wrong, their continued employment at that airline may soon be under discussion.
For an FO to include a statement like what's in the OP in his briefing would send a pretty strong signal that he's looking for an opportunity to do that, expects that it may be at least somewhat likely that he'll need to do that, or something similar.  Given that he probably has less experience than the Captain, that's a pretty extreme attitude.
I've had trips as an FO that felt like a multi-day check ride, and they're no fun but sometimes that's just the nature of the Captain (typically, a wanna-be check pilot) you fly with.  For an FO to suggest that the Captain is going to be getting a multi-day evaluation by someone junior and less experienced... well, that probably wouldn't go over very well.
There are plenty of ways for an FO to communicate that they are competent, professional, and by-the-book, without coming across as hostile or aggressive.  A statement like what's in the OP wouldn't be in that category.

Probably not OP's intent, but I've definitely heard urgent transfer of control being briefed in a IOE/training situation. It's certainly important there to avoid dual control mishaps.


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What do European pilots use for IFR enroute charting (besides Jeppesen)?
Is there something equivalent to FAA IFR enroute charts for European countries, where you can see published routes, holds, minimum altitudes, etc?  I can find terminal area procedures in the AIPs, but the Eurocontrol enroute charts contain hardly any useful information.

All countries publish relevant information in the national AIP. Some include charts, others mainly publish textual information. It is then up to chart providers (Jeppesen, Lido etc.) to compile the data into relevant charts. It might be easier to answer your question if you specify which exact information you are looking for

Welcome to aviation.SE! This question is very similar, although I'm not sure it adds much to what you already know.

@expeditedescent So if I don't want to pay the ridiculous prices for Jepp charts in Europe, what are my options for enroute flight planning?

All the info you need is published in the national AIPs. Most of which are freely available online

Thanks, I am just getting used to where everything is in the AIPs (because we don't use them in the US).  I was looking at Eurocontrol, but now it seems obvious I'd find them in the ENR section.

In Europe, like in most of the world, IFR enroute charts are published in ENR 6 of the national AIP, which can be found notably from Eurocontrol @IS online. Some countries publish these charts in sections ENR 3.x.
Some countries like Spain even publish electronic charts.
More details (route data tables) about IFR routes are published in the following sections:

ENR 3.1 Lower ATS routes
ENR 3.2 Upper ATS routes
ENR 3.3 Area navigation (RNAV) routes
ENR 3.4 Helicopter routes

Note: this organisation of routes will change soon.
There are numerous companies offering flight manuals beside Jeppesen and Lido: Navblue is one example.


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Could one see stars from Concorde in daytime?
Concorde flew to an altitude of 60,000 ft (18.3 km) where stars should be visible at noon, aren't they? This question asks on how high stars become visible, and it is said Blackbird pilots could see them at 80,000 ft. Concorde flew at the Armstrong line when highest, above more than 90% of the atmosphere's mass. Are there reports of passengers and pilots on Concorde seeing stars (other than the Sun) when at peak altitude? Also, did the Sun appear whiter due to the thinner atmosphere?

You can see Sirius from sea level. Climbing to 18 km doesn't change anything, still only Sirius. "The daylight visibility of stars has been investigated for an observer altitude of 100 000 ft, using published visual threshold data and calculated sky luminance. Venus, Jupiter, and Sirius, plus Mars at its brighter phases, can be detected with the naked eye", source. Sirius has a magnitude of -1.46 at sea level. At night an eye can see down to +6 only. Someone may build an answer starting with these elements.

@Someone -- there's nothing wrong with referring to the Concorde as "the Concorde", even if the accepted usage (for some weird reason, no other plane is treated this way, and this has been the subject of an ASE question https://aviation.stackexchange.com/q/57085/34686) is simply "Concorde".  IMHO that was a totally superfluous edit (version #3).

@Someone-- actually, I forgot that you were the one who bountied that question not so long ago. Thanks, that was nice-- but I still do feel the recent edits are superfluous.

@quietflyer okay, I won't change it in old questions anymore. If I'm editing one anyway for another reason, should I change it then?

Your call-- I'd prefer you not on my own question, but I only asked one question about the Concorde, so prob won't be an issue. Thanks for replying.

Tell ya what: I'll attach a camera to a model rocket, put the biggest engine I can find on it, take it up in a plane and shoot that sucker out the window (or any available opening) and we'll see what the camera says. (I apologize for my informal language)

Yes, in at least one exceptional circumstance.
The book Racing the Moon’s Shadow with Concorde 001 describes a 1973 scientific flight that remained in the moon's umbra for more than an hour, in daytime.  As stars are quite visible from the ground during a solar eclipse's totality, they would have been even more visible from a 17 km altitude.

I don't think the question was asking about a solar eclipse! Even though it's technically "in daytime", the question is clearly about normal daylight.

I don't think so, either!  But I couldn't resist, that flight was just so cool.

@CamilleGoudeseune Sorry but during a total eclipse you can see them even from the sea level as you say yourself. :-)

This page has some images of the view from the Concorde. On one image two stars can be seen. So obviously one could see some.

Can't tell which photo you're referring to as having stars in it. Also, FWIW, even at midnight photos that size have a hard time depicting individual stars - they're just so tiny & pretty dim. Doesn't mean that stars are, or aren't, there for the eye to see, just that they're hard to capture in small photos with nearer (and much brighter) objects in view & in focus.

Is this answerer a duplicate account of the questioner's?

@RalphJ On the image on which you only see the horizon, no Concorde window and no Concorde wing, only the Earth from cruise altitude. You can see a star on the upper left and another on the upper right of the dark sky. Or at least I assume it are stars.

@CamilleGoudeseune Yes it's me.

https://meta.stackexchange.com/help/merging-accounts fyi

Those specks look both too large and way too bright to be stars.  They're basically as bright as the clouds in daylight, and stars aren't nearly as bright as that.  Try taking a picture of the night sky on a clear, dark night with your phone's camera... you might get individual stars, but probably not.  Now try it with something moderately bright (like that cloud layer) in part of the photo... the camera won't see stars at all. I'd strongly suspect those specks are either on the camera lens or the aircraft window.

@RalphJ What would cause this specks? When taking an image of the sky from within a spacecraft, it may happen that you get stars visible on it as there is the window in front of the camera. https://upload.wikimedia.org/wikipedia/commons/3/30/STSCPanel.jpg

What would cause the specs? "I'd strongly suspect those specks are either on the camera lens or the aircraft window." - @RalphJ

@FreeMan So what would cause them? As you can see in the linked image, the stars can look 'way too bright' on it.

The white specs in the left-hand image of the 2nd row of pics could be stars, but they could just as easily be some dust or a scratch or pit on the window. That's exactly what Ralph J said. The array of spots on the right-hand image in that row (inside the cockpit) is definitely something on the window itself.

@FreeMan I agree with what you say about the cockpit image to the right, and this is what made me feel unsure if the dots in the other image are actually stars. But orbs of dust usually look like large circles. I hope someone can shed light on this.

"The specs" may be ice crystals, but one picture seems to have a star or planet visible.  We'll have to put in for a "moonroof" design on Concorde II for a more definitive answer.

@RobertDiGiovanni The Concorde II is currently being built by Boom Technology. It is important that it has good windows so one can see anything outside with one's own eyes, unlike in the Spike S-512 which wouldn't have windows but use cameras instead, and you wouldn't know whether it is something outside or an ice crystal on the camera's objective.


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How did the CVR of Bashkirian Airlines Flight 2937 keep recording after the collision?
Black boxes are in the back of the plane.
The CVR microphone is obviously in the front.
When the tailfin of DHL 611 split Bashkirian 2937 into two just ahead of the wing, I would expect the recording to stop straight away.
Yet here you can hear the first few seconds after the collision. How?

The official report says it even recorded for almost 2 min: "The CVR of the TU154M was a four track analogous tape device, which had recorded the last
30 minutes of the accident flight. After the collision, the CVR recorded for a further period of 01:55 minutes."

Your assertion that the CVR is in the back of the plane must be incorrect.

A CVR has no wireless capability. So clearly the CVR in Flight 2937 was somewhere forward of the location where the plane was split in half.
It is common for the CVR to be placed fairly far aft, but it certainly doesn't have to be.


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How does the A350/380 operate on Variable Frequency AC generators?
To keep a constant frequency of 400 Hz, most aircraft have a CSD (Constant Speed Drive) associated to the AC generator. On most types (e.g. A320, A330, B737, B747, B777) an Integrated Drive Generator (IDG) is used. This unit is simply a CSD and an oil cooled generator inside the same case that provides this fixed frequency output.
Sometimes we even use a variable-speed constant-frequency (VSCF) generator, that provides AC power at constant frequency using a tap converter.
The A380 and A350 have variable-frequency electrical generator, with no CSD or IDG. How can they work without a fixed AC frequency? If the fixed AC frequency is not needed, why it is needed in all the other aircraft types?

If you worry about the frequency not being constant, first ask the question: why is the frequency important at all?

400 Hz systems typically rely on transformers to produce all required voltages. I guess A380 designers were none too keen on installing an extra ton of soft iron in their airplane.

Not specific to aviation but general electric equipment: AC with a consistent frequency is important whenever you transmit power through solenoids directly fed from mains voltage. Now, traditionally, this included almost everything except primitive devices based on resistive heating (including light bulbs). Motors obviously need to generate alternating electromagnetic fields to push their rotors, and most electronic devices can't just operate with the given supply but need some specific voltage levels: the simplest way to achieve that is a transformer. In either case, reliable AC frequency is needed if you want it to work efficiently.
But these electromagnetic devices have their problems – they're big/heavy (more so in 50/60 Hz than in 400 Hz) and inflexible. If you need to change the speed of an AC motor, you need to either use an asynchronous model which does not have the precision of a synchronous one, employ inefficient step-down techniques or even mechanical gearing. Similarly, changing voltage in an LF transformer (or keeping it constant when the input fluctuates) is only possible with tricky-to-operate coil taps, or with wasteful resistive power-burning.
Over the last decades we have gained powerful, efficient, compact HF switching solid-state circuitry which can largely solve all of these issues, and doesn't depend on any fixed AC input (neither frequency- nor voltage-wise). It basically uses always DC (first rectifying the AC, if necessary) and then internally generates AC of whichever frequency is optimal for the application. This allows quickly stepping motors at any speed and precision to degrees, as well as feeding sensitive electronics with just the right voltage, without significant losses or input-fluctuation sensitivity.
So when none of the consumers really cares for 400 Hz anymore, you might as well allow that frequency to change too, if it means the necessary power can then be generated more efficiently.

@leftaroundabout In a nutshell, now we can use variable frequency because we have better solid state rectifiers and users less sensible to feeding frequency. Am I wrong?

@GianniAlessandro right, that's what I think is the dominant reason.

Rectifiers are a small part of the puzzle. The important part is that modern power electronics are much better than they used to be. Modern power converters can efficiently connect your variable frequency variable voltage generator to a fixed voltage DC bus. Some of them can even move power bidirectionally so your generator can double up as a starter.

A VFG on a A350 (Variable Freq Generator) ranges from 360Hz to 800Hz (idle to takeoff) but it weighs less than a traditional IDG or CDS due to the fact that it has less components inside since it does not need to convert the freq to a fixed 400Hz. Most components that use AC convert the variable frequency to a fixed 400Hz anyway.
The output of the generator is actually 230VAC , so you can go with a higher gauge wiring for even more weight reduction.
At the end of the day its all about weight reduction. The A350 also has a 5000 psi Hydraulic system because by upping the pressure you can use a smaller diameter of titanium tubing.

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How is a near miss defined?
With respect to mid-air collisions, how is a near miss calculated, detected, and reported?  Does ATC have radar detection, or is it strictly up to pilots to report a close encounter with another aircraft?

As you wrote in the question body, they're called "near mid-air collision" (or NMAC), not "near miss", if you change the title fast we might avoid the George Carlin references... woops, too late. ;)

My first thought was to ask the question, why is it called a near miss?  I used the term near miss since it seems to be a more common phrase and thought that would be pertinent to the answer.  Plus, I want to know about a near miss, not a far miss.

It's called a near miss because the planes came near to each other but missed. It's a miss that was near, not something that was nearly a miss.

At small, busy airports, where most NMACs occur radar is not accurate enough in many cases to judge the situation and it must be done by eye. At large airports or in low visibility the separations are much wider to support radar and therefore NMACs are much less common.

First I'd just like to comment that "near miss" is a bad term (as falstro also noticed). It seems to say that the planes "nearly missed", implying they didn't miss. The FAA uses the terms "Near Midair Collision" (NMAC) for serious incidences, and "loss of separation" for less serious ones. As such, terms like "near miss", "close call", and "narrowly escaped disaster" are not well defined.
ATC does usually have radar. The data is recorded and can be analyzed later. Of course, not all areas have radar coverage. In these cases it is up to pilots to report if they feel safety was compromised. They can use the Aviation Safety Reporting System, which is part of the Aviation Safety Information Analysis and Sharing system.
Especially with commercial flights, Traffic Collision Avoidance System (TCAS) is also used. If TCAS issues a Resolution Advisory (RA), which commands pilots to take action to avoid a collision, the pilots are usually required to report the incident.
A "loss of separation" would be anything less than the required separation.
According the the FAA:

A near midair collision is defined as an incident associated with the
  operation of an aircraft in which a possibility of collision occurs as
  a result of proximity of less than 500 feet to another aircraft, or a
  report is received from a pilot or a flight crew member stating that a
  collision hazard existed between two or more aircraft.

That and more information about reporting incidents can be found in Section 6 of the AIM.

You can look up "near miss" in a dictionary. It means "narrowly avoided collision or other accident". So the OP is not using the term incorrectly.

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Why have different pattern altitudes for different aircraft?
In the FAA AFD for Santa Rosa airport (KSTS), the pattern altitude is given as 1,000’ AGL for small aircraft, and 1,500’ AGL for large aircraft.
Why do these altitudes differ? Doesn’t it compromise having a uniform pattern altitude so aircraft can see each other?

Several possible reasons.

Speed differences between aircraft classes. Larger jets cruise and land at much faster speeds than single-engine props. Keeping their pattern separate from slower traffic minimizes problems posed by a faster plane entering the pattern behind a slower one.
Noise abatement. A jet, even a smaller private one at near-idle in approach, is loud. Keeping them higher increases the distance and number of thermal strata to shield nearby residents from traffic noise.
Prevailing instrument conditions and relative pilot experience levels. A ceiling below 1000 feet, the small craft pattern altitude, would ground VFR flights and thus drastically reduce the number of small craft in the first place. Jets, turboprops and other larger planes are much more likely to be IFR-capable (plane and pilot) and so they're placed higher because they can deal with clouds in the pattern (the airport, if towered, would likely alter pattern height to clear cloud layers but traffic holding above the clouds would still require an IFR approach).

Larger aircraft generally are faster and fly wider patterns than small planes. It would be much more difficult to sequence different types of aircraft at the same altitude while maintaining separation.

Additionally to KeithS' answer, you also have some airfields in e.g. Germany, where a different pattern exists for glider aircraft, ultra-lights and regular single or multi engine pistons. The consideration here is not only speed, but also the ability to maintain level flight. Glider patterns in almost all cases will be very close to the airfields with little impact on surrounding housing areas, as gliders generally create less noise than powered aircraft. They also need to remain closer to the airfield in the pattern, as they can only trade speed vs altitude, but not gain altitude or maintain it as power aircraft. Powered aircraft can follow a pattern that will be suitable for noise abatement and other requirements, such as obstacle clearance or avoiding certain areas for other reasons.
The same consideration that apply above between gliders and powered aircraft do apply between slow powered aircraft and fast powered aircraft, as already explained in the other answer.

gliders generally create less noise than powered aircraft -- under what circumstances would a glider create more noise than a powered aircraft???  :)

@FreeMan Never tested it, but a glider at high speed in a slip could create more noise than a powered aircraft in idle and a clean flight? Gliders can be noisy as well, but they usually are flown not to be noisy. :D

Ah. The only thing I could think of was the glider going through someone's bedroom window would likely make more noise than the C172 passing overhead. Your answer sounds... safer.

@freeman A glider through someone's bedroom window is a hell of a racket...

@SentryRaven - Good one; you see this in the U.S. as well. A few dirt strips out in the exurbs of DFW have rules regarding different pattern directions for low-noise (gliders, ultralights) versus high-noise (everything else); gliders are allowed to circle over the denser neighborhood on one side of the strip while the higher-noise powered planes have to stay over the fields and farmhouses to the other side.

Gliders fly on the opposite side of the airfield or inside the power pattern not because they can't maintain level flight, but in order to stay out of the way of faster power traffic.

At many of the airports I've flown in (as a helicopter pilot), they will also have rotorcraft fly in the opposite direction from fixed wing. Our descent profile and cruising speeds are different than aircraft, and given that we may do confusing things like slow down into a hover, its for the best. Generally they'll place us at a different altitude as well.
As other people mentioned, the fact that larger planes travel at different speeds is one reason they may place them in a different pattern, and I suspect it helps with wake turbulence as well. The planes can be spaced a bit closer together if large planes aren't comingled with the smaller aircraft.
Similar setups will also happen in commonly used airways. For example, where I live in Chicago, and when flying westward through Midway/O-Hare airspace (they overlap), they'll generally have us fly along the highway. They tend to put the rotorcraft at a much lower altitude than the fixed wing, which I suspect is not only for the same reasons as above, but also because the altitude minimums for rotorcraft are lower than for fixed wing, and it gets more traffic out of the way.

FAR § 91.126 (b)(2): "Each pilot of a helicopter or powered parachute must avoid the flow of fixed-wing aircraft". That's for Class G, but tower controllers understand why.

And do you mean "opposite direction" or "opposite side of the runway"?

I meant opposite direction. So fixed wing will depart in a left hand pattern, and rotorcraft a right hand pattern. My downwind leg is on the opposite side of the runway of fixed wing.

Ok we call that opposite side. Opposite ditection would be 13/31 or 06/24


text:
Why tail wheel rather than tricycle?
I'm working towards my tail wheel rating and enjoying it greatly. But, people ask me why some planes have a conventional landing gear (tail wheel).
Why indeed? I understand perhaps why they had them originally, but is it just historical reasons? Seems like maybe it can have slightly lighter gear and perhaps simpler design, but I'm wondering if there are deeper reasons.

possible duplicate of Why do most aerobatic aircraft have conventional landing gear?

the dup is for aerobatic aircraft, this is for aircraft in general.

@Peter if there is a near dup it is good to mention it in your Q and explain why your Q is different.

Just FYI it's a tailwheel endorsement not a rating.

@JimA depends on jurisdiction and type of license.

@falstro Yes, but he is based in California.

I've read in other SE meta forums that generally speaking, duplicates are usually assigned from the more specific q to the more general. So, if there is a good answer posted to this question, the acrobatic q should be marked as dupe to this one, since this one is a more generalized question.

Ratchet freak gives already most of the reasons. I might add that on a grass field the taildragger is easier to handle. The relatively high drag and long lever arm of the tailwheel or skid will help to pull the aircraft straight at low speeds when rudder control power is low. On a hard surface, however, the tricycle gear is easier to handle. Also, not only the weight, but also the drag of two wheels is less than that of three.
If you look at modern airplane designs, those where weight must be kept low (like aerobatic planes) still have a taildragger gear. It is also used in gliders and motor gliders, because they will operate mostly from grass strips and do not want to include internal space to accommodate three retractable wheels.
Big taildragger designs from the early days vanished with the emergence of concrete runways from the 1930s on and the need to brake more during rollout when wing loadings and landing speeds went up. On concrete runways, the tricycle gear handles better and gives much better visibility. Without the ability to brake hard, the rollout lengths of  taildraggers would prohibit todays wing loadings. With retractable gears the drag disadvantage is no more, and the increased weight can be tolerated.

It's a fiery debate.
One of the reasons for the taildragger design is indeed weight. There is also that the plane will naturally sit at a positive angle of attack and will keep the propeller further off the ground. Rotation is assisted by gravity because the CoG is behind the wheels. Also getting a tailstrike on takeoff isn't critical.
The reasons for the nose wheel design is increased control during takeoff (with the tail dragger there is a period where the tailwheel is off the ground and yaw control is up to the rudder)

Some nose wheel gears are fragile and would not survive well on unpaved runways.  Also the distribution of weight is a factor.  There is less weight on a tail wheel than a nose wheel.  Therefore most of the weight of a conventional gear aircraft is split between the mains.  Use of a conventional gear on an soft runway eliminates the issue of the nose wheel digging into the surface.


text:
Are there countermeasures for semi-active laser homing SAM?
I would imagine sensors that pick up the wavelength/PRF and a couple of emitters trying to flood the seeker. Or could chaff be sufficiently reflective?

Is there a reason that you think this exotic / expensive method is even necessary when trying to shoot down a helicopter?   I think you have two questions here. The first is about countermeasures for semi active laser homing in a SAM.  The second is the utility of using laser illumination to target a helicopter, whether it be SAM or AAA in use.  Suggest you split them up, and link them to each other as related.  Lastly, why are you bringing Chaff into a discussion of IR sensors?  I ask particularly given the user name that you have chosen. ;)

Welcome to Aviation.SE.  Please take the [tour] and visit the [help] to see how to get the most out of a Stack Exchange Q&A site.

@KorvinStarmast The idea was that a lack of countermeasures might make this method attractive. But since it doesn't appear to be, I was wondering about practicality too. I split the questions up as you suggested. So is chaff not able to distract the seeker by reflecting IR radiation?

Your call yourself Flare. Look up the term "IR Flares."

Dazzling the seeker might work. Chaff won't, because it won't stay in the line between the emitter and the target, and the detector on the launch platform (which may not be laser (lidar), but might be passive radar or IR camera) is unlikely to be fooled by a decoy. But best defence against anything semi-active is shooting the launch platform.

I’m not aware of any type of AAA or SAM system which uses laser guidance.

There is one I know of is QW-3. Quoting from Wiki: " The gyro stabilized seeker provides very high degree of accuracy and is extremely effective against low altitude cruise missiles. "

@KorvinStarmast And how exactly would IR Flares perform Pulse Repetition... Passive IR guidance is not the same as semi-active laser guidance.

@CarloFelicione Both the RBS 70 and the Starstreak do, although they are both beam riding.

@JanHudec The idea was that, If the launch platform is the emitter, a well timed chaff deployment could reflect onto an incoming seeker and provoke its premature detonation.

@Flare, the thing is that the launch platform won't be easily fooled to track the chaff rather than the actual target (it has human operator, computer good enough to understand inertia and viable turn radii, or both), so since the laser produces narrow beam, it would only illuminate the chaff if it lingered directly between the emitter and the target, which is only possible if the target is flying directly from the emitter. But usually the defences will be engaging incoming aircraft.

Related

Ground targets do have countermeasures against laser guided munitions in the way of smoke screens, for example on the Shtora-1 or Arena Active Protection Systems. These disperse an aerosol that reflects the light frequency of the known enemy laser designators.
This works against laser homing missiles like the AGM-114 Hellfire (except the Lima, which is radar-guided) by effectively displacing the aim point of the guided munition to the smoke cloud and giving the target a chance to reposition out of line of sight of the launch platform.
Note that this is less effective against beam riding missiles like the 9K121 Vikhr which has the laser sensors on the rear of the missile and does not depend on the reflection of the guiding beam, but rather on its orientation.

On the topic of aerial targets, the situation is very different. In the first place, there are not many anti air systems that rely on laser guidance, since these are only occasionally useful against rotary wing threats and close to useless against fixed wing.
The two most likely situations where a helicopter might find itself being targeted by a laser guided munition are the result of improvisation: it can be engaged by another airborne platform with and air-to-ground weapon or by an armored vehicle using an ATGM.
The likelyhood of this happening is considered low enough that many helicopters do not have an LWR to alert them of such a threat. As far as I am aware, it seems that Russian designs like the Ka-50/52, Mi-24 and Mi-28 do have dedicated LWRs while western designs tend to include more general MAWS equipment. The main advantage of the separate system is that it can potentially detect tank rangefinders that illuminate the airframe trying to obtain a firing solution for the main gun.
Secondly and more to the point, smoke screens in the air are not an option as they would require the helicopter to remain in a hover, which would make it an easier target for precisely the kind of laser guided systems you want to defeat, among others. It is much easier to maneuver behind terrain to disrupt the guidance beam, which is easier if the helicopter has forward airspeed.
You may be thinking of something akin to chaff corridors, coordinated lines of chaff deployed by dedicated ECM aircraft in advance of air raids in the WW2 and Cold War period. These clouds of chaff were meant to jam radar stations and were not dense enough to hinder optical or IR systems:

Even in a hover, the rotor wash would tend to disperse any aerosol cloud pretty quickly. Nice discussion of the concepts involved!


text:
Why do thrust vectoring nozzles delay?
I saw a video demonstrating the SU-30's thrust vectoring nozzles and noticed that the horizontal stabilizers begin moving up/down before the nozzles do. It seems that the F-22 also has this delay.
Then, after it's in an upright/downright position, if the pilot brings the stick back to center, both the nozzles and the stabilizers move at the same time. This leads me to believe that this is probably not some mechanical lag that causes it. So, why is there that initial delay?
SU-30:

F-22:

Photo demonstrating this delay (note how the nozzles only begin moving some milliseconds after the stabilizer starts moving):

I don't think you can/should rule out mechanical reasons. If the system is hydraulic then it makes sense. The aircraft can not "anticipate" when the pilot will move the stick away from the neutral position, so this delay may be the time it takes to build the required hydraulic pressure to actuate the nuzzle

On the other hand, another possible reason is that the designers did not want the aircraft to be too sensitive and/or "finicky" to control. Just because there is a delay on the ground/low altitude does not mean there is a delay at all altitudes/flight regimes.

I have read that such thrust systems can be non-minimum phase control problems, meaning they have to get further from the goal before getting closer.  What you are seeing might be a side effect of that.  Here's a paper describing one control system which has a non-minimum phase transfer function for a ducted fan, which is pretty close to a vectored thrust jet engine.


text:
Which "warnings" are issued when a military aircraft is going to enter foreign airspace?
There are reports in the media saying Turkey shot down a Russian military aircraft after ignoring several warnings and after they entered Turkish airspace.
Which "warnings" are these? Are they standardized somehow?

they pick up the radio, set it to the desired frequency/ies and start yelling "get off my lawn!"

This depends on the rules of engagement for a country and how the intercepting aircraft are instructed to act.
Radio Contact
The intercepting aircraft will try to establish radio contact on the distress frequencies available. 121.500 MHz or for NATO aircraft 243.000 MHz.
Visual Contact
Unless there is an imminent threat, the intercepting aircraft can position next to the intruding aircraft and establish visual contact with the pilots. There is also standardized procedures, such as the infamous rocking of wings.

(Image Source: www.cfinotebook.net)
Flares
Unless at high altitude, ground based units can shoot flares to attract attention and inform aircraft that they are entering prohibited or restricted airspace.

From this answer, I understand that they would have been warned possibly by flares and through radio on 121.500 (is this frequency used by all aircraft? I was assuming it was for civilian ones only); since Russia and Syria (the country which the alleged intruder was coming from) are not NATO countries. Is there any standard phraseology? I discard visual contact as this would require Turkish aircraft to enter Syrian airspace "just to warn".

@orique The answer lists possible methods. AFAIK from reports, the Turkish F16 only used radio to contact the Russian aircraft while they were still in Syrian airspace and bound for the Turkish airspace. 121.500 MHz is used by military and civilian aircraft. Military aircraft can tune it in at least, as otherwise interception of civilian aircraft would be difficult.

@orique Note that any country has the right to defend their sovereign airspace. This is why so much of the debate is focused on where the aircraft was shot down, since that is of primary interest from an international legal standpoint. Rules of engagement are as far as I'm aware national law (although possibly standardized across NATO), not international law.

Actually the true debate is focused on where the aircraft was at the point the missile was fired. The political debate is focusing on where the aircraft was when it was hit, but that isn't necessarily the same place in aircraft capable of mach 1+

"the intercepting aircraft can position next to the intruding aircraft and establish visual contact with the pilots". By giving him "the bird"? ;)

@JonStory I guess that even that may become a point of discussion: is the point where the missile is fired more important than the point where the missile hits? Either country may develop a different opinion on that subject, depending on what turns up in investigations.

I doubt that's truly up for debate: legally speaking the point when the missile is launched is all that really matters, although I've no doubt the difference will be ignored when used for political point scoring. Essentially, Turkey is perfectly entitled to shoot missiles at anything over their territory: any other detail is down to the national law of Turkey.

and remember that this was far from the first incidence of Russian military aircraft violating Turkish airspace and being warned away. A prudent Russian commander would have put in place ROE ensuring his aircraft stayed well clear of that border. Unless of course he had explicit orders from Moscow to provoke a confrontation.

It's a basic tenet of international law: If an aircraft is above your territory, you can shoot it down - the airspace belongs to that nation. If the aircraft breaks the law of that nation, while in the airspace of that nation, the laws of that nation apply (a basic tenet of sovereignty), see http://www.icao.int/Meetings/atconf6/Documents/WorkingPapers/ATConf.6.WP.080.1.en.pdf which mentions this. If the aircraft subsequently leaves your airspace after you've fired the missile, how are you meant to prevent that? Missiles aren't instantaneous.

There's no requirement to stop your missile just because it leaves your airspace. Although equally, your neighbours are entitled to shoot your missile down as soon as it crosses their border. What happens in your airspace is your business. The point is that when the decision was made to fire the missile, the Su24 was a legitimate target according to Turkish rules of engagement and international sovereignty. You could program a missile to be deactivated, but would you really want to? It would be open to abuse ("hopping" the border to waste ammo) or malicious acts (GPS jamming, for example)

"What happens in your airspace is your business": This didn't happen in the Turkish airspace, that's the point of canceling missiles. As the hit occurred over Syria, would that entitle Syria to shot the Turkish fighter over Turkey, for the sake of the same principle, and so on... (that's not an actual question, I'm mostly ok with your comment).


text:
What is the brace position for cockpit crew?
I have read a number of times the CVR transcript of US Airways 1549. Just before impact, they say:

we're gonna brace

I know what is the brace position for passengers, but I'm not sure about how cockpit crews would adopt it. For Airbus aircraft (as this flight was) I think it could be done more or less the same way as passengers, but what about in Boeing or other yoke-equipped cockpits? Wouldn't the brace position interfere with critical flight controls?

In the film Sully (2009) the brace position of the pilots was depicted as placing the palm of the free hand on the rim of the instrument panel, keeping the arm straight. During this time the captain was depicted as still operating the side stick with his left hand. I cannot confirm if this procedure was accurately depicted or not

(I meant 2016, not that it matters significantly)

You don't brace -- you're still operating the aircraft!  The pilot seats have shoulder harnesses; in many cases you can lock them, plus they also have inertial reels that keep you from slamming forward at an impact.  Additionally, the pilots can presumably see the moment of impact coming, and tense for exactly that moment in a way that passengers cannot.

Bob Hoovers alleged quote comes to mind: "If you’re faced with a forced landing, fly the thing as far into the crash as possible".

Yep -- I was thinking about the very last second before impact. Maybe the harness is not enough to restrain your head, and they mentioned bracing. That caught my eye.

@orique I'm not sure how precise it is as it's "just TV", but in many Mayday series you see pilots getting head injuries after impact, presumably from hitting some of the instruments on impact.

Tensing the body's muscular system is generally counter productive in a crash. Bracing is helpful and a different concept.


text:
What is the proper procedure for a piston engine fire on the ground (e.g. during engine starting)?
I am wondering what is the correct sequence of action if there is a fire e.g. during engine starting. Of course I know that there are emergency procedures in each AFM and every single plane is different etc. but I am thinking about "general" set of actions.
Let's say that an aircraft has a fuel shut off valve and mixture control - like a little Cessna. What should we do if an engine catches fire during start-up - shut off the fuel valve and mixture to idle cutoff, or remain mixture and cut off fuel valve (and still try to start the engine)?
Please help me out what are the correct steps.

As you said, the "proper" procedure is whatever is in the aircraft's operating handbook. Having said that, there is a general pattern, at least based on a few POHs I have to hand. Note that they all list the procedure as "engine fire on startup"; there's no general "engine fire on the ground" procedure.
The 'generic' steps are:

Continue cranking as usual to pull the fire and fuel into the engine
If the engine starts: let it run for a few minutes then shut down as normal and inspect the aircraft for damage
If the engine doesn't start: open the throttle, cut off the fuel (mixture, fuel pump, and/or fuel cutoff as applicable), and evacuate the aircraft

Here's an example from a Cessna 172S POH (Lycoming IO-360-L2A engine); bold items are memory items:

Ignition Switch -- START, Continue Cranking to get a start which would suck the flames and accumulated fuel into the engine.

If engine starts:

Power -- 1800 RPM for a few minutes.
Engine -- SHUTDOWN and inspect for damage.

If engine fails to start:

Throttle -- FULL OPEN.
Mixture -- IDLE CUT OFF.
Cranking -- CONTINUE.
Fuel Shutoff Valve -- OFF (Pull Full Out).
Auxiliary Fuel Pump Switch -- OFF.
Fire Extinguisher -- ACTIVATE.
Engine -- SECURE.   a. Master Switch -- OFF.   b. Ignition Switch -- OFF.
Parking Brake -- RELEASE.
Airplane -- EVACUATE.
Fire -- EXTINGUISH using fire extinguisher, wool blanket, or dirt.
Fire Damage -- INSPECT, repair damage or replace damaged components or wiring before conducting another flight.

I love it that part of the checklist is to fix the plane before trying to fly it again!  I might have forgot that part--

@quietflyer Perhaps that checklist item was written by a lawyer :-)

Why release the parking brake?

@TomMcW So that if the plane has to be towed - either to get a burning plane away from buildings or a dead plane out of the way of traffic (taxiway or runway) - it can be towed easily.

If you hear a "foomp" during cranking, that's a backfire that could create a fire, so you keep cranking and hope it works out.  Once you can see smoke/flames swirling around from the cockpit, there is an open gasoline-fed fire under the cowling and it's way too late for cranking to help.  You'll just secure the plane and get the hell out without delay and either start fighting it with your little extinguisher, or stand back and watch.


text:
Wing moment - providing stability or not
It is said that wing alone is unstable, because it provides a nose up moment, so tailplane is needed to damp it. But normally wing provides a pitch down moment (as far as I know, apart from very high aoa situation) because centre of pressure is behind the centre of gravity. So shouldn’t wing moment be actually stabilising? I’m confused about stability, because we one time we consider stationar lift acting in aerodynamic centre and moving centre of gravity, next time moving centre of pressure with stationary centre of gravity and so on... please help me out.

The question could use some clarification--

You stated

But normally wing provides a pitch down moment (as far as I know,
apart from very high aoa situation) because centre of pressure is
behind the centre of gravity.

If we are using the archaic "Center of Pressure" concept-- as opposed to the newer concept of an "Aerodynamic Center" combined with a "pitching moment"-- then we can observe that the Center of Pressure of the wing moves forward as aircraft pitches up (increases angle-of-attack), and moves aft as the aircraft pitches down (decreases angle-of-attack).  This is clearly destabilizing.
Assuming we are speaking of an aircraft flying in a trimmed condition, your observation that the center of the pressure of the wing is behind the Center of Gravity of the aircraft is in fact true, if the horizontal tail is creating a downforce.  But this does not imply that the aircraft would still be stable if we removed the horizontal tail.
It appears that you may be making the mistake of assuming that the wing's Center of Pressure is operating at a fixed location behind the CG of the aircraft, regardless of changes in angle-of-attack.  If that were true, that would imply that the aircraft would tend to pitch down to a lower angle-of-attack whenever the airspeed increased, and would tend to pitch up to a higher angle-of-attack whenever the airspeed decreased.  That wouldn't be a stable situation either.

Okay, one more question - instability does not mean the moment must be up or down, it must be a moment that cannot be balanced, either pitch up or pitch down, right?

It's not about the moment but its change with AoA.
Any wing can be trimmed when the cg is at the center of pressure. What counts is how things change when AoA changes.
If you want stable behavior, use an inverted airfoil. A regular, cambered airfoil will cause unstable behavior.
For a trimmed airplane the moment around the center of gravity is zero. Now it is important how this moment changes when the airplane moves away from this trim point. If AoA increases and the moment becomes negative (nose down), the airplane is stable.
If the center of gravity is too much forward, the airplane cannot be trimmed in the first place because control authority is insufficient to produce enough downforce at the tail in order to compensate for the pitch-down moment of the lift force on the wing around the more forward center of gravity.

Okay, 2 questions - instability does not mean the moment must be up or down, it must be a moment that cannot be balanced, either pitch up or pitch down, right? And too forward CoG may also cause a pitch down moment that cannot be balanced, yes?

@Konrad What counts is the change in the moment. Does it become smaller / more negative with increasing angle of attack (and vice versa), then the airplane is stable. A trimmed state means the moment is zero around the CoG. Once the airplane moves away from the trimmed state, the change in the moment determines whether the airplane is stable or not.

I'm going to try a mental analogy exercise that I hope the experts on here will accept. Leaving out many of the complex moments and forces at play, just for the purposes of conceptualization by the layperson or semi-layperson. See if it works.
It's important to separate stability and trim.
Static stability in pitch, in very crude terms, is really just a "vertical weathervane effect".
Take an airplane, locate its center of mass, and turn it sideways and stick it on a spike on a tall pole, with the spike on its center of mass and the sideways airplane free to pivot on it, nicely balanced on the spike.  As long as the aerodynamic center of the entire body, fuselage, wings, and tail, the point where aerodynamic forces acting on all those surfaces is focused (the Neutral Point), is aft of the spike, the airplane will point into wind, like a weathervane. And if the wind shifts, it will move to point into the new wind direction. It's positively stable in its weathvane-pointing.
Move the spike back so that it's coincident with the Neutral Point, and it will no longer weathervane and will just want to point any which way independent of the wind.  It's weathervaning stability is neutral.  Move the spike farther aft to behind the Neutral Point, and my weathervane plane will want to switch ends - its weathervaning stability is negative.
In other words, the Neutral Point wants to trail the C of G if there is any offset between them, and if it's right on the C of G, it doesn't want to do anything and the body is free to drift aimlessly.  Positive static stability requires the Neutral Point to seek to trail the C of G in the correct orientation.
Turn the whole thing back level again, and the same thing is happening except that the wind's changes in orientation is vertical instead of horizontal, and we call it Angle of Attack.  When the change occurs, the airplane, being a free body, rotates about the CG (where the spike was) to keep its orientation into wind, to maintain a certain Angle of Attack, as long as the Neutral Point of the plane is aft of the C of G.  The Neutral Point wants to trail the C of G, in the vertical plane, and the airplane is positively stable.
Trim is process of creating a variable balance of forces between the fore and aft lifting surfaces that allows the "pointing angle" of the overall body to be adjusted relative to the air stream.
Going back to the vertical plane-on-a-spike, if the wing and tail surfaces are all aligned, the whole thing will point into wind straight, with no angle off the wind.  If I change the incidence of the tail surface to generate a lateral force, it'll rotate the plane out of wind until an opposing force from the front surface, the wing, applies a moment that cancels out the one from the rear surface. My sideways airplane weathervane will now orient itself with into wind with some offset, say 5 degrees off the wind, and will rotate when the wind changes to point with that 5 degree offset. This is because, when the wind changes, the balance of forces between the main and aft surfaces that created the 5 degree offset is skewed, one force is stronger than the other, and it seeks to rotate to restore the force balance, which occurs with the 5 degree offset.
Turn it back horizontal and it's the same, except that the offset wind pointing is now a vertical orientation, Angle of Attack.  When the tail surface's incidence is moved to position X, an imbalance of forces is created relative to the wing, and the plane pitches, about the C of G, until the pitching forces of the wing opposing the forces of the tail are back in balance, and the plane flies with an offset to the airstream, an Angle of Attack.  Being able create any required stability point Angle of Attack allows us to make the wing make lift that supports everything without having to have it on a horizontal pole with a spike on it to hold it up.
If I set the horizontal tail to achieve a balance of forces with the wing at a 5 degree offset, the body will rotate in the vertical axis to maintain that 5 degree offset, or Angle of Attack. If I change the incidence of the tail to create more force, the equilibrium point is changed, say to 10 degrees, and the plane will point in the vertical plane, to maintain the equilibrium point that is now found at 10 degrees.  And because the Neutral Point is in it's correct location aft of the C of G, it will positively seek to regain that 10 degree Angle of Attack if the vertical wind orientation changes.
We have positive static stability at our trim Angle of Attack (to the pilot, trim speed, since speed and AOA are directly connected), and if I move the stabilizer surface to another position, our stability will be relative to a new Angle of Attack (and speed), and the plane will actively seek to achieve and maintain that new Angle of Attack thanks to the Neutral Point's offset from the C of G.


text:
Is "balanced field" defined with or without an engine failure?
I’m wondering what exactly means a balanced field in terms of aircraft performance. From what I know it means that TODR=ASDR, also it is minimum field length required. But I do not know whether this TOD and ASD are with or without engine failure.

It refers to the case with an engine failure.
The balanced field length is exactly equal to the accelerate-stop distance and the accelerate-go distance, if the V1 speed is chosen, where those two distances meet:

2.3.1.3 Balanced Field Defined
[...]
The Continued Takeoff—After an engine
  failure during the takeoff roll, the airplane
  must continue to accelerate on the remaining
  engine(s), lift off and reach V2 speed at 35 feet.
  The later in the takeoff roll that the engine
  fails, the heavier the airplane can be and still
  gain enough speed to meet this requirement.
  For the engine failure occurring approximately
  one second prior to V1, the relationship of the
  allowable engine-out go takeoff weight to V1
  would be as shown by the “Continued Takeoff”
  line in Figure 10. The higher the V1, the heavier
  the takeoff weight allowed.
The Rejected Takeoff— On the stop side of the
  equation, the V1/weight trade has the opposite
  trend. The lower the V1, or the earlier in the
  takeoff roll the stop is initiated, the heavier the
  airplane can be, as indicated by the “Rejected
  Takeoff” line in Figure 10.
The point at which the “Continued and Rejected
  Takeoff” lines intersect is of special interest. It
  defines what is called a “Balanced Field Limit” takeoff.
  The name “Balanced Field” refers to
  the fact that the accelerate-go performance
  required is exactly equal to (or “balances”)
  the accelerate-stop performance required.

(FAA Pilot Guide to Takeoff Safety, emphasis mine)
The continue case (accelerate-go) assumes an engine failure one second prior to V1.

New pilots in jets will tend to think "gotta rotate now!" when "Rotate" is called.  This is a problem in non-slatted jets that are less forgiving to over-pitching.  Thing is, technically, you're in the go-no-matter what phase having passed V1 and the runway ahead is no longer required for braking, so you can take your time rotating, within reason.

The only thing I would add to the graph would be limits on how low or high V1 can be.  V1 will never be lower than Vmcg as you would not have directional control for engine failure after V1.  V1 would also never be higher than VR as you will never start rotating and then abort the takeoff.

The Take Off Distance (TOD), Take Off Run (TOR), Accelerate Stop Distance (ASD), by definition, take into account both, the engine failure and the all engines scenario. Read FAR § 25.113 Takeoff distance and takeoff run for the definitions.
A balanced field calculation forces us to limit the maximum weight of the airplane so that none among the TOR, TOD, and ASD exceed the actual Rwy length. It does not change the way TOR, TOD, ASD are calculated.
To  understand the significance, or need for, the term "Balanced Field" has the makings of a  substantial discussion of it's own.


text:
Selecting radials for radial interception
I’m a beginner in intrument flying so sorry for my ignorance. Few months ago I was doing BIR training and with my CFI we were intercepting radials, we were doing that on HSI (Garmin G500).
He told me that If I want to intercept radial inbound I should set the tail of the needle to the desired inbound radial and if I want to intercept radial outbound I should set the head of the needle to the the desired outbound radial.
My question - is this way of setting desired radials correct? Because I read somewhere that we always should set the head of the needle to the course that we mean to fly, no matter if it is outbound or inbound - to avoid reverse sensing.
So if I want to intercept and fly radial outbound 180 I should set head of the needle of my HSI on 180 and if I want to intercept and fly radial 240 inbound I should set the head of the needle of my HSI on 240. Now I'm confused, please help me out.

Did you intend for there to be a difference between the terms "end of the needle" and "arrowhead"?  Because there are two ends, and I think you may both be saying the same thing...

You are right, I didn't know how to call it properly to be honest. Arrowhead is the "forward end" like the one that shows your heading on gyro, the end of the needle is the "end end".

If it helps, the terminology I have always used is simply "head" and "tail".  The head should always match your intended direction of flight.  Always.

Your instructor is correct - using his method, means you do not have to do any reciprocal course/heading/plus/minus 180 calculations - instead you must remember "Radial 050 outbound" set the head (arrow/course) on 050. "Radial 160 inbound" set the tail on 160 which means the head/arrow/course will be on 340. It's evident that you have to simply use the Radial as spoken by ATC and acknowledged by you without further calculation.
@Konrad, going back to your last paragraph

"So if I want to intercept and fly radial outbound 180 I should set head of the needle of my HSI on 180 . . . ."

So far, so good! but

". . . and if I want to intercept and fly radial 240 inbound I should set the head of the needle of my HSI on 240. Now I'm confused, please help me out."

but your instructor told you to set  the tail of the needle to 240. Had you done this, the head of the needle of your HSI would be on 060 which is the course you must fly.
So your thought process should be like this:
"OUTBOUND" -> SET HEAD TO CLRD RADIAL - INTERCEPT AND MAINTAIN.
"INBOUND" -> SET TAIL TO CLRD RADIAL -> GLANCE AT HEAD TO READ OFF CRS + CONFIRM IT IS CONSISTENT (~RECIPROCAL) WITH THE HEADING TO BE FLOWN -> INTERCEPT AND MAINTAIN.
In either case, after these initial actions make a cross-check using pencil and paper or looking at a chart and the pilot in the other seat (if any) to maintain situational awareness (SA).
Some food for thought about nomenclature:
Better to say "cleared radial" rather than "desired radial".
When it's a HSI style display call it head/tail of "course selector" rather than "needle", (as compared to an RMI style display which has needles)

This is a terminology problem - and I think you're actually both right but you need to learn the terminology. Radials always radiate out from the VOR.
You should absolutely always set the needle to the heading you intend to fly in order to avoid reverse sensing.
However, if you're intending to "fly inbound on the 240 radial" then you're actually on the reciprocal heading of 060 - which is what should be set on your OBS. The flag should indicate "TO".
If you're flying outbound on 180 then you should set 180 on the OBS and the flag should indicate "FROM".

Well, all of you (and, the instructor) are correct for using your own technique on the aircraft in which you are familiar. The technique can vary depending on your equipment. So let’s clear up a few things.

You can not get reverse sensing with a properly working HSI (which the G500 should have). This is because the HSI should always orient the displayed heading (or, top of the instrument / lubber line reading) with the actual aircraft’s heading. You will only get reverse sensing when the indicated course or radial at the lubber line and the actual heading are in opposite half’s (top and bottom) of the instrument. This happens in a VOR OBS with a movable card since the desired radial is always at the lubber line.
The technique described by the OP makes sense. It completely ignores the “To/From” Indicator on the VOR which confuses some beginners. It sets the HSI up to indicate only To when you are inbound and From when you are outbound regardless of which side of the VOR you are on. It also has the added benefit of always aligning your Radial arrow with your desired course and heading. Similar to how it will be when you are lining up for your final course on an ILS or localizer. This will also avoid reverse sensing in a regular VOR OBS indicator. When you learn to properly use the HSI, you might stop using this method. Although it may behoove you to stop using it now since there will be VOR questions on the written Knowledge Test which will require you to have intimate knowledge of the VOR OBS and HSI.
Another method to use for the long run is to always place your desired radial to intercept in the course window to move the point of your needle to that degree. Then note where the To/From indicator is pointing. It will always point in the direction of the VOR. Upon intercepting the radial, turn towards and fly in the direction of the To/From indicator if you want to go inbound to the VOR. This method has the added benefit of giving you situational and spacial awareness of where you are in relation to the NavAid since the radial needle will always be pointing down the radial like an extended center line. And, the To/From indicator dispels ambiguity.

He told me that If I want to intercept radial inbound I should set the
tail of the needle to the desired inbound radial and if I want to
intercept radial outbound I should set the head of the needle to the
the desired outbound radial.
My question - is this way of setting desired radials correct? Because
I read somewhere that we always should set the head of the needle to
the course that we mean to fly, no matter if it is outbound or inbound
to avoid reverse sensing.

Both of these statements are true. By setting the tail of the needle to a desired inbound radial you're flying in the direction of the head of the needle.

So if I want to intercept and fly radial outbound 180 I should set
head of the needle of my HSI on 180

Correct

and if I want to intercept and fly
radial 240 inbound I should set the head of the needle of my HSI on
240. Now I'm confused, please help me out.

This is wrong.  If you set the HSI needle (aka course bar)  on 240 you are in fact planning to fly the 240 radial outbound, in the direction of the arrow.  If you want to fly it inbound then put the tail on 240 so that you're flying the reciprocal direction (060) which is pointing the arrow toward the beacon.


text:
Can wingtip vortices formed around an unswept wing produce vortex lift?
Vortex lift is a kind of aerodynamic lift force due to vortices formed along the leading edge of highly-swept (usually 60 degrees of swept angle or higher) wings at high angles of attack. The "vortex sheet" is high in rotation speed and thus low in pressure, which provides the pressure difference, resulting in lift. *in subsonic speeds

"Vortex sheets" causing vortex lift
Normally an unswept wing (without wingtip devices)would have wingtips that can easily form vortices, called wingtip vortices. This kind of vortex is associated with higher induced drag, and is often avoided by adding wingtip devices like winglets. However, is it possible that wingtip vortex can also produce vortex lift? If so, why try so hard eliminating it?

I am a student pilot and just curious about different means of lift production. In addition to my question description, unswept wings produce lift with laminar, attached flow, at higher angles of attack, the vortices would cause stall. While vortex formed around highly-swept wings would help with lift generation at certain situations. I haven't looked into this a lot, so I would really appreciate a precise, simple answer.

Just a couple of clarifications: "vortex sheet" is the vorticity sheet released behind the trailing edge of a wing. Wingtip devices do not avoid induced drag nor the formation of tip vorteces but have more or less the same effect of extending a bit the wingspan.

Vortex  at straight wing has very small contact area with wing and also at wrong position.
Vortex has low pressure, you can see blue color on upper surface where vortex touch surface. This part of wing has backward orientation, so this produce more drag than lift.
Pressure leak(light blue/green color) at wing tip area reduced lift more then this little increase of lift due to vortex. End plate/winglet reduce this pressure leak.

Does winglet also reduce drag?

@Frank Reduce induced drag but increase skin friction drag. https://aviation.stackexchange.com/questions/8556/is-a-winglet-better-than-an-equal-span-extension

The picture you've chosen of a water tunnel test at Onera nicely shows how the vortices generated at the leading edge of the delta wing wash over its upper surface and coalesce to form two big vortices, one on each side of the wing. Those vortices help the airflow in remaining attached to the wing so that lift can be generated till very high AoA, as it can be seen for example in the following plot taken from this NASA report:

The 62° delta wing tested at subsonic speeds generates lift till some 30° while a "standard" rectangular or swept wing would stall at maybe half of that angle.

is it possible that wingtip vortex can also produce vortex lift?

The same vortex phenomenon happens also on a "standard" wing but! their coalescence takes place well behind the trailing edge, where the wing is already finished and the effect of generating lift till very high AoA has therefore no time (or space) to develop.
Anyway this is not the only important characteristic of those vortices: in general, when a vortex rolls up along a direction parallel with the chord, it generates also a force aligned with it i.e. drag by definition. This drag is termed induced drag. The vortices seen on the delta wing make no exception: if on one hand they help the airflow in remaining attached, on the other hand they increase drag as well and quite a lot.
So it becomes now quite interesting to compare the polar of that delta wing with the polar of a standard swept wing (the plot for the latter is taken from this second NASA report):

Let's compare for example the points at $C_l=0.8$. For the delta wing it corresponds to a $C_d$ of 0.2 while for the swept wing it corresponds to a $C_d$ of some 0.07: that means that at the same lift coefficient a delta wing generates some three times more drag then a swept wing! That's why the Concorde had to takeoff with the afterburners on and that's

why try so hard eliminating it.

Let's ... um ... make a winglet out of the second ... and ... have it on the end of a straight wing!

@RobertDiGiovanni: is it a question? I don't understand it, can you please reformulate it?

It's an unswept wing question.  But your data confirms why the Vulcans needed an armada of tankers to cross the Atlantic.

Ah now I understand it  I would say that the polar for a rectangular wing is basically the same as the swept one, maybe the stall region would be a bit delayed.

The vorticity behind a wing is only a consequence of what happened before above and below the wing, but cannot alter the wing's lift or drag in any way.
I remember a breathless report of an ultralight flying wing called Kasperwing which could fly extremely slowly thanks to a stationary vortex which formed on the upper side of the wing at high angle of attack.
Wikipedia calls it a bit more soberly a

fully controlled, completely stalled parachutal descent mode

which was made possible by the airfoil shape. Note the "descent" part: This did not make straight or even climbing flight possible but needed to be bought with a high rate of potential energy loss.
Other than that, no, vortex lift is the prerequisite of highly swept leading edges.

If wingtip vortices don't alter the wing's lift or drag in any way, then what is the purpose of installing wingtip devices like raked wingtip, to eliminate wingtip vortices, as an unmodified wingtip should produce more lift than a specially-shaped raked wingtip?

@Frank Marketing. Mostly. They do help by spreading the vortex sheet slightly and lowering local vorticity, but most of the vorticity remains. None of them even comes close to the claimed "elimination" of wingtip vortices. Note that this claim is not made by engineers, but by marketing. That should tell you something.

Not sure if wingtip devices are all marketing? Wingtip vortices don't cause induced drag, that's correct, I totally agree with you on that, but those vortices do affect lift distribution and drag negatively, in my understanding. Check out this question also: https://aviation.stackexchange.com/questions/96338/how-is-blended-winglet-better

@Frank My answer was referring to all those wingtip devices pointing up or down. A raked wingtip is actually quite clever, see https://aviation.stackexchange.com/questions/19073/how-does-the-raked-wingtip-of-the-boeing-787-work/19078#19078. But I do not consider a raked winglet a wingtip device. It is a characteristic of a wing planform.

Just to clear any misunderstandings. So winglets and other wingtip devices DO reduce drag and other negative effects provoked by wingtip vortices?

@Frank Why do you insist that wingtip vortices "provoke" drag? They don't. Drag happens due to local pressure on forward and suction on rearward facing parts of the structure, and of course due to friction on both. That's it. And wingtip devices add weight and have a wetted surface, so they "provoke" their own share of induced and friction drag. Only when they produce more thrust than what they cause in drag will they be helpful. And that is mostly at high lift coefficients, but not over the full envelope.

Yes, but only at higher angles of attack, which generally have lower overall airfoil lift to drag efficiencies.
Straight wings use Hoerner wing tips to push the vortex away from the wing tip.  This allows the entire span of the wing to be productive in lift and away from turbulence.  Ground effect also creates a similar result by strengthening the outflow from higher pressure under the wing.
However, soaring birds which, by virtue of the updraft contributing to their higher relative wind Angle of Attack, take full advantage of wing tip vorticies not only to create lift, but also thrust$^1$.
But, as airspeed and the Reynolds number increases, better lift to drag ratios can be had with higher aspect straight wings at lower angles of attack, where wingtip vorticies are less prominent.
$^1$ in much the same manner as sailboats create forward motion into the wind


text:
What does this part on a vertical stabilizer do?

On a B787 vertical stabilizer shown in the image, there's this small fin at the leading edge that connects to the fuselage.
It seems too small in size to be considered a dorsal fin. Simply adding this small fin at the leading edge will only increase the sweep back, and thus reduce the vertical stabilizer effectiveness.
I am assuming that this is for improving structural strength? Or does it have other purposes?

@Jan please don't answer in comments, instead put it in an answer so it can be voted on and it can be accepted.

@sophit I do not think so, this fin seems too small in size to be considered a effective dorsal fin

@Frank: sorry, wrong link, I meant this one

...thus reduces vertical stabilizer effectiveness

Any area added increases stabilizer effectiveness.  The structure is similar to a strake on a wing.
The area where fins (and wings) attach to the fuselage can be a source of drag.  Wind tunnel studies can show improvements by shaping these junctions in certain ways.
The greater sweep of the strake can also improve the stabilizing characteristics at higher angles of relative wind, such as in a cross wind gust, where a straight stabilizer might stall.

It this case it's more likely the designer liked the look of a gradual transition. There is a little bit of "styling" going on. or there is a duct that needs to run up there that needs to be enclosed.

@JohnK Apart from aesthetics, as someone in the comments previously mentioned, this gradual transition may also have the effect of reducing interference drag here.

If the intersection is 90 deg or more, interference drag isn't supposed to be a thing. It's why you often don't see fillets on wings that meet the fuse at a 90 deg angle, like a Corsair.

@JohnK the upper part of the fuselage (when the aircraft has a positive AoA) may be a different world than a wing juction.  Vertical stabilizer design is an interesting field.  Many of the variable sweep shapes of 1930s vertical stabilizers (such as from the B-17) became ... the "ogive" of the Concorde.  I guess "it depends" what shape is ultimately best for a given application, but it does seem to have something to do with off-center relative wind.

Beyond transonic considerations, sweeping the fin moves the aerodynamic center aft without extending the fuselage. Also it looks cool. Most GA airplanes got swept fins in the 60s because of the look. Going from the straight tail to swept tail made no detectable difference whatsoever to the handling or performance of the 172. Strictly styling. Other problem is, as you increase the sweep angle, rudder displacement starts to have a pitch up effect.

@JohnK yes, it does look good.  I actually had some good results with  square Vstabs on my FF models (so did the Vikings with their ships).  I don't think it matters much with the 172, but have a look at the Fokker D7.  Strakes on both the vertical and horizontal stabs and winglets at the ends of the upper wings.  They knew something about high AoA flying.

@RobertDiGiovanni Those are just fixed stabilizers surfaces where the triangular shape is most structurally efficient when you make it from tubing. The wing tips are just aileron aerodynamic balance horns that provide a mass balance location (if one is used) and also lighten aileron forces.

@JohnK Is this gradual transition( wing root fairing) https://www.flickr.com/photos/a380spotter/5643760646 here also for styling only? Does it have aerodynamic benefits?

@Frank At very high speeds yes, it can help, as with the Citation 10 https://en.wikipedia.org/wiki/Cessna_Citation_X#/media/File:Cessna_750_Citation_X_AN0983363.jpg  where they provided a really exaggerated fairling ahead the wing box going under the fuselage. But looking at the wing root on the C-10, you can see it just has a straight joint with the vertical side of the transition fairing. In the A-380 the fairing in the pic is also likely enclosing plumbing like bleed ducts, etc. When I say "styling", there is always going to be some attention to aesthetics. Designers are humans.

Sort of interesting that one can't "wash out" a straight vertical stabilizer (on  both sides), so the sweep may give it a less sharp stall.  As for horizontal stabilizers, why not give them slats and Fowler flaps too ;-).  And sweep is aesthetically appealing.


text:
Does the obstruction in a propeller duct increase exhaust pressure or decrease pressure/increase speed?
I came up with this question when looking through the answer for this question, which states that a convergent duct(obstruction) compresses the exhaust so that its pressure matches the ambient pressure. In the comments section another question was answered like this:

Q:Doesn't the pressure decrease and the air accelerate when the diameter decreases ?
A:The pressure decrease happens in the obstruction and after it - it's increased by the obstruction, between the fan and the nozzle exit.

I am a bit confused by what's meant by "pressure decrease in the obstruction" and "pressure increased by the obstruction". What really is the effect of converging the duct, increase exhaust speed to decrease static pressure or compressing exhaust to increase static pressure?

For a convergent nozzle the exit area will not change the jet pressure or velocity if the fan pressure ratio is the same. The major effect will be on the mass flow; a smaller nozzle area will let less air pass through.
For a complete system the fan pressure ratio and adiabatic efficiency will change with mass flow (the fan compressor map shows you the curves), so if we immagine to keep the same RPM of the fan and gradually shrink the nozzle aera, the pressure ratio will increase and so will the exit velocity.
A consideration on the thrust:
Remember that thrust is, as a fist order approximation, the product of mass flow through the fan times the difference between velocity at the exit of the nozzle and free stream velocity (how fast the propeller is moving in the air). So reducing fan nozzle area will slightly increase the speed but greatly reduce mass flow
------ EXAMPLE ------
Here I will  write a simple example for clarification
Before starting I want to remind that Static Pressure is what it's commonly known as pressure while Total Pressure is the pressure that the fluid would have if you brought it to a complete stop.
Let's imagine a ducted Fan moving at a speed of Mach 0.25 with a exit area of 0.01 m^2 at sea level condition, with a compression ratio of 1.3 and adiabatic efficiency of 0.6:
$M_0 = 0.25\;;\; A_{exit} = 0.01\: m^2 \;;\; T_0 = 228\: K \;;\; p_0 = 103205\: Pa\;;\; \pi_{fan} = 1.3 \;;\; \eta_{fan} = 0.6  $
For air ideal gas constant are $R = 287\; \frac{J}{kg\; K} \;;\; \gamma = 1.4 $
From the Mach number and pressure we can calculate the total pressure and temperature for free stream condition:
$p_{t0} = p_0 (1 + \frac{\gamma -1}{2} M_0^2)^{\frac{\gamma}{\gamma-1}} = 107791 \: Pa \\
T_{t0} = T_0 (1 + \frac{\gamma -1}{2} M_0^2) = 291.6 \: K$
From the fan pressure ratio and efficiency we can compute total pressure and temperature behind it
$p_{t2} =  \pi_{fan}\cdot p_{t0} = 140128 \: Pa \\
T_{t2,iso} =  \pi_{fan}^{\frac{\gamma-1}{\gamma}}\cdot T_{t0} = 314.3 \: K \\
T_{t2} =  \frac{T_{t2,iso} - T_{t0}}{\eta_{fan}} + T_{t0} = 329.4 \: K$
Now we let expand the fluid up to atmospheric conditions
$p_{4} =  p_{0}\\
T_{4} =  (\frac{p_{t0}}{p_{t2}})^{\frac{\gamma-1}{\gamma}}\cdot T_{t2} = 301.8 \: K\\
M_4 = \sqrt{\frac{2}{\gamma -1} (\frac{T_{t2}}{T_{4}} -1)} = 0.676$
The speed of sound at the exit nozzle and jet velocity are
$a_4 = \sqrt{T_{4}\gamma R} = 348.2 \: m/s \\
V_4 = a_4\cdot M_4 = 235 \: m/s$
the mass flow of the fan is
$\dot{m} = \rho_4 \cdot V_4 \cdot A_{exit}\\
\rho_4 = \frac{p_4}{R T_4} = 1.191 \: kg/m^3  \\
\dot{m} = 2.799 \:kg/s$
The thrust of this fan is
$Thrust = \dot{m}(V_4 - V_0)\\
V_0 = \sqrt{T_{0}\gamma R}\cdot M_0 = 85 \:m/s \\
Thrust = 419.8 \: N$
You can see how only the mass flow depends on the exit area, if we half the area, the mass flow and thrust are halved. In reality the parameter $\pi_{fan}$ would also change, maybe going from $1.3$ to $1.45$. If $\pi_{fan}$ increases $V_4$ also increases, but it isn't enough to compensate for the reduction in mass flow.

Sorry it’s a bit hard for me to understand. A converging nozzle should keep the mass flow rate constant by increasing flow speed, and with the mass flow rate constant, this speed increase should also increase the velocity difference, thus increasing thrust. Is there anything wrong with my understanding?

What you say is true only for very small variation of the exit area (5% max). I added an example for more clarity.

It depends where in the system you look.  Think a narrowing in a pipe.
That which moves the fluid must work harder to maintain mass flow. Pressure in the pipe before the narrowing increases.  Velocity and pressure in the narrowing increase and decrease respectively.
The issue was that the apparatus in question gives less thrust per unit energy input than a free propeller under the conditions tested.


text:
Why does a flat plate create less lift than an airfoil at the same AoA?
This picture of the lift curve slopes for four-digit NACA airfoils and a flat plate is from another question on this topic. It shows that at the same positive AoA, a flat plate generates less lift compared to the NACA airfoils.

An airfoil and a flat plate both creates a low pressure region above; for an airfoil it is suction-induced, and for a flat plate it is due to a separation bubble. Since the (high) pressure distribution below these two are similar, from an arbitrary guess, the lift force generated should at least be the same for both. But why does a flat plate create less lift than an airfoil at the same AoA?

Any "airfoil" that performs no better than  a flat plate wouldn't be useful or interesting.  Only those shapes that do better than the simple flat plate get any consideration or use as airfoils. So is your question why such airfoils can exist?  As in Bernoulli and all the "what produces lift" discussions? Or is there a different line of inquiry here?

@RalphJ My question is why such airfoils exist. I'm not asking about how they produce lift, as that has been mentioned in my question, but why are those airfoils better, and how they produce MORE lift.

In the photo in the linked question you can see that the incoming air flows up and over the turbulent area, with an aerofoil without separation at the same angle the air above the wing is directed downwards much more efficiently therefore generating more lift

It shows that at the same positive AoA, a flat plate generates less lift compared to the NACA airfoils.
From an arbitrary guess, the lift force generated should at least be the same for both

Your guess is right, a flat plate develops exactly the same lift as any other airfoil (at least until stall begins). So, why that difference in the plot?
Convention
The AoA is measured in respect to the geometrical line connecting the leading edge with the trailing edge of the airfoil. By an aerodynamic point of view this line has no special meaning. So why do we use anyway this line to plot the aerodynamic coefficients? Because this line is easy to trace and unmistakable and therefore makes things easy to compare (actually this geometric line does posses an aerodynamic meaning but only for symmetric airfoils since it coincides with the line of zero lift for obvious reason of symmetry).
Now, the NACA airfoils of the 44xy series considered in your picture is a cambered one i.e. an airfoil generating lift already at negative AoA (some -5° in that plot - but remember that this -5° is just a geometrical convention and has no aerodynamic meaning). Anyway a flat plate is not cambered rather symmetrical by definition and therefore its lift coefficient is always 0 at 0° AoA: this comparison is unfair! Indeed, if you shifted the plot of the 4412 to the right so that it also starts by 0 lift at 0°, then you would get an almost perfect overlap with the coefficient of the flat plate.
Or... we can simply make a fair comparison from the beginning and use another symmetrical airfoil like any of the NACA 00xy series, for example the ubiquitous NACA 0012 which has the following coefficients:

Here (blue line) you can see that it develops for example a $C_l$ of 0.5 at 5°, just like the flat plate in your plot. And, being symmetrical, it obviously also goes through the point of 0 lift at 0°, again just like the flat plate.
Ok, but if a flat plate generates the same lift as any other symmetrical airfoil why the horizontal tailplane of a jetliner is built around a NACA 0012 and not a simple flat plate? Because of the stall characteristics: a flat plate begins to stall already at around 5 to 10° while the NACA 0012 at 22° and that's the most important improvement introduced by an airfoil in respect to a simple flat plate.

For a symmetrical airfoil, is the pressure force vector always perpendicular to chord, like the flat plate? If so, when we look at this from the perspective of pressure force, how can the symmetrical airfoil delay stall while a flat plate cannot?

"how can the symmetrical airfoil delay stall while a flat plate cannot?" The answer is: smoother recovery pressure on the rear part of the airfoil with a consequent more stable boundary layer.

Why different shapes react differently to a fluid flowing past them is ultimately subjective, trying to fit one abstract model to several of these shapes.
How they react is purely a matter of measurement.
Values of x for "because x" include post-stall flow separation, the Coanda effect, Reynolds numbers, (non-)laminar flow, the oversimplifications in children's textbooks, etc, etc.
In this case, where the question has veered to "pre-stall, why does camber increase lift," the intuitive reason is that camber deflects more air downwards.

Sure, if C_L = C_L.  The why-because generalization here is that, all else being equal, more camber means more downwash, which means more lift.